This invention relates generally to tires and a method of manufacturing them. More particularly this invention relates to a tire which does not have a cord reinforced carcass.
Cord reinforced tires of rubber or other rubberlike materials having the reinforced plies extending from bead-to-bead require a number of manufacturing components and steps and are thereby fairly costly and/or time consuming to produce. In an effort to reduce the manufacturing costs and/or time involved there has been an effort to produce cast tires.
Some cast tires have been made with the same cross-sectional shape as the cord reinforced tires. Some have been disclosed as being with and without reinforcing tread belt plies and with and without rubber treads, while having a cast body. Some have advocated decoupling from the sidewall from the tread, such as disclosed in U.S. Pat. No. 4,006,767, Pneumatic Tires, while others advocate providing a rib in the shoulder region of a tire as shown in U.S. Pat. No. 4,305,446.
It is known that when cast tires are made with the same general cross-section as the cord reinforced tires the walls of the tires must be made with a substantial thickness to provide the necessary strength and support. The increased wall thickness is undesirable because it increases the weight and cost of the tires as well as causing higher operating temperatures.
Furthermore, cast tires have experienced problems in durability and sidewall growth.
Unreinforced cast bodies are isotropic, that is they have equivalent properties in the x, y and z directions, because they are homogeneous. Isotropic materials when subjected to stress along one axis transfer a significant portion of that stress along the other axes. In contrast, a radial tire, by virtue of the reinforcing carcass cords is not isotropic. Loads carried by these cords transmit a smaller portion of these stresses to the rubber and the other axes.
Furthermore, when an isotropic cast carcass is subjected to radial loading there is a tendency to resist this and thereby prevent the tire from attaining a deflected contour similar to that attained by radial tires. In other words, the tire resists bulging of the sidewall which increases lateral squirm.